A method and apparatus for calculating dialysis efficiency is disclosed in Swedish Patent Application No. 9702074-7, filed on Jun. 2, 1997, by Gambro AB. In this Swedish patent application, a whole body relative efficiency is calculated. The calculation uses a removed urea concentration curve obtained by a urea monitor during dialysis treatment. The urea monitor measures the concentration of urea in the effluent fluid from the dialyser, normally emitted to the drain. The result obtained by the urea monitor is a value of the removed mass of urea mrem as well as the removed urea concentration curve, from which can be calculated the total accumulated urea mass m0 in the body, whole body dialysis dose Kt/V, solute removal index SRI, etc.
According to this Swedish patent application, it is necessary to obtain a value of the initial concentration of urea in blood in order to be able to fully characterise the dialysis treatment. Another approach, also described therein, is to obtain a value of the total body water volume V of the patient, whereupon the urea concentration in the blood of the patient may be calculated.
A number of different approaches to obtain the initial concentration of urea are given in this Swedish patent application, such as blood samples or equilibrated dialysis solution before the start of the treatment. These methods are more or less problematic and there is a desire to eliminate manual intervention. Moreover, blood samples need to be taken before initiation of the dialysis treatment. As soon as the treatment starts, the initial blood concentration of urea is diluted due to cardiopulmonary recirculation and access recirculation. Thus, care must be exercised to obtain the initial urea concentration before it is compromised.
The object of the present invention is to provide a method and apparatus for obtaining the initial urea concentration in blood before the dialysis treatment, to be used in the invention according to Swedish Patent Application No. 9702074-7 for calculating the essential dialysis related parameters of a patient.